Focused ultrasound temperature effect in tissue-mimicking material and sheep liver

The location of High Intensity Focused Ultrasound (HIFU) beam in a tissue medium is an important parameter in assessment of the thermal field as it influences the temperature rise in the tissue. Our hypothesis is that the location of the beam can be affected by the power of the transducer. HIFU procedure with 30s of sonication time was performed at different powers of transducer (5 to 60 W) as well as different initial locations of beam in a tissue mimicking material. Eight thermocouples were embedded at 4 different layers in a phantom to measure the temperature rise during HIFU procedure. An inverse method based on experimental data and optimization algorithm was used to find the actual location of beam based on the experimental data. Our experimental data showed that for a higher power (60 W) as compared to a lower power (5 W), the focal distance that the actual position of beam moves away from its initial location increased with the raise in power. Thus, beam location can change at different powers of transducer. Using inverse method we showed that there is a direct linear correlation (R2 = 0.95) between the transducer power and the distance that beam moves away from its initial location. Therefore, it is of great clinical importance to study the effects of transducer power on the location of HIFU beam in an attempt to minimize the damage to healthy cells.

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Temperature Rise in Tissue Mimicking Material During HIFU Procedures

ASME 2007 Summer Bioengineering Conference ◽

10.1115/sbc2007-176922 ◽

2007 ◽

Author(s):

Subhashish Dasgupta ◽

Prasanna Hariharan ◽

Matthew R. Myers ◽

Rupak K. Banerjee

Keyword(s):

Temperature Rise ◽

Focused Ultrasound ◽

Acoustic Power ◽

Tumor Ablation ◽

High Intensity Focused Ultrasound ◽

Tissue Temperature ◽

Invasive Technique ◽

Operational Parameters ◽

Tissue Mimicking Material

High Intensity Focused Ultrasound (HIFU) has shown considerable promise as a minimally-invasive technique for various therapeutic applications such as tumor ablation and vessel cauterization. The efficacies of these HIFU procedures depend on various operational parameters such as total acoustic power, pulse duration and transducer dimensions. In this study, the effect of total acoustic power on the tissue temperature rise is studied both experimentally and numerically. Experimentally, HIFU ablations, at different acoustic powers, were carried out in a tissue mimicking material embedded with thermocouples. Temperature rise measured from the in-vitro experiments were then validated with the numerical computations. Results show that experimental and numerical temperature rise match accurately. Our numerical model was able to predict the peak temperature rise within ∼12% of the experimental results. Results also show that the tissue temperature rise is linearly proportional to the input acoustic power. For the acoustic power levels considered in this study, the results suggest that acoustic non-linearity does not play a major role on the tumor ablation procedure.

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